Banquo says that the witches have beards, so they don’t seem like women.

When Banquo and Macbeth meet the witches, they do not seem like creatures of the earth. They don’t look human, and they don’t look like either men or women. Banquo is disturbed by the presence of beards.

You should be women,

And yet your beards forbid me to interpret

That you are so (Act 1, Scene 3, p. 12)

Besides the beard, the witches are just creepy. The men are disturbed by them, or at least Banquo is. Macbeth is curious. He weighs everything in terms of what we can gain, so he is looking for what the witches can do for him. He is therefore not as repulsed by them as Banquo.